In the letter sold yesterday, dated 1954 and written in German to philosopher Eric Gutkind, Einstein said he did not believe in God.

A 1939 letter in which Einstein warned then United States president Franklin D. Roosevelt about Germany's atom bomb preparations was auctioned for $2.1m in 2002.

"For me the unadulterated Jewish religion is, like all other religions, an incarnation of primitive superstition", the letter also said. "And the Jewish people to whom I gladly belong, and in whose mentality I feel profoundly anchored, still for me does not have any different kind of dignity from all other peoples", Einstein wrote.

Gutkind's book "Choose Life: The biblical Call to Revolt" characterizes Judaism and Israel as ethically untouchable entities. In it, Gutkind proposed a reinterpretation of traditional Judaism.

Einstein was unequivocal in his critique of Gutkind's book in his letter.

The letter fetched almost double the auction house's predicted price of up to 1.5 million

The letter had been held among Gutkin's papers, but it came up for auction in London in 2008. The bidding for the letter ended at £170,000 ($217,000), with evolutionary biologist Richard Dawkins among the beaten bidders.

Acknowledging his disappointment in failing to secure the item, Dawkins said: "This letter was about something very important to Einstein I suspect".

The letter has thus been cited as evidence of Einstein's atheism, but at other points in his life the famous mathematician himself dismissed the label.

According to Einstein: A Life, a biography published in 1996, he was devoutly religious as a child.

Specifically, Einstein did not believe that if there was a God, he answered individual prayers and intervened directly in human affairs. This god "reveals himself in the lawful harmony of the world, not in a God who concerns himself with the fate and the doings of mankind".